This invention constitutes an improvement over the recuperator structure described and claimed in co-pending patent application Ser. No. 09/934,640 filed on Aug. 22, 2001 by William R. Ryan entitled “Recuperator For Use With Turbine/Turbo-alternator”, published and commonly assigned to the same assignee of this patent application and incorporated herein by reference. While the structure disclosed in the aforementioned patent application describes an annular recuperator for an annular combustor, the invention is essentially a heat exchanger that can be configured in other configurations such as annular, square, rectangular, etc.
Scientist and engineers have spent a great deal of time and effort for improving heat exchangers and particularly those used with microturbines. As one skilled in this art appreciates, the recuperator for the microturbine is one of the most expensive components of the system and it typically is constructed from relatively thin sheet metal with a portion thereof being preformed into corrugated sheets or fins. The fins and sheet metal sub-assemblies are typically brazed. In the microturbine environment the recuperator serves to preheat the compressor discharge air entering the combustor by being placed in indirect heat exchange relation to the turbine exhaust. Because the recuperator operates in a hostile environment, namely the relatively high pressure air discharging from the engine's compressor and the relatively hot exhaust (1000 degrees Fahrenheit (° F.)) discharging from the turbine, the manufacturing of the recuperator is complex and difficult and requires considerable effort to assure its long life.
The recuperator described in the aforementioned patent application is an annular recuperator consisting of a plurality of involute shaped cells circumferentially spaced between a plenum divided into a cold and a hot chamber and an outer adjustable shroud. Each cell is sealed and includes an inlet header and inlet and an outlet header and outlet axially spaced relative to each other. The spaces between cells essentially define straight-through passages and a plurality of fins are mounted in these spaces between the cells and since the fins are flexible they conform to the involute shape. (The outer configuration of this assembly resembles the shape of a stator vane typically used in gas turbine engines). In operation, the compressor discharge air flows into the plenum and is directed into the cells via the inlet in the inlet header of the cell and is discharged into the hot chamber through a discharge port associated with the discharge header. The space between the cells provides a straight-through passage flowing the turbine exhaust placing the exhaust in indirect heat exchange with the cooler air in the cells. The heat picked up by the compressor discharge air by conduction is transported to the inlet of the combustor where it is combusted with fuel and delivered to the turbine at a temperature approximating 1500° F.
While the purpose of the structure disclosed in the aforementioned patent application is to reduce leakage and costs and, in fact, compared to heretofore known structures, it meets these objectives, this invention is intended to reduce the possibility of leaks and costs even above those obtainable by the recuperator described in the aforementioned patent application and the prior art. This invention eliminates the use of fins both in the cells and the spaces between cells without degrading heat exchange efficiency and improving heat exchange efficiency. This, alone, will reduce the number of locations necessary for brazing and the number of component parts, which, of course, contributes to the reduction of the costs both in parts and labor.